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GC use BatchResolveLocks may miss some pessimistic locks in rare cases #45134
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The issue is confirmed as a bug.
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…iss primary pessimistic locks (pingcap#45143) close pingcap#45134
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Labels
affects-6.1
affects-6.5
affects-7.1
affects-7.2
severity/major
sig/transaction
SIG:Transaction
type/bug
The issue is confirmed as a bug.
Bug Report
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This problem is introduced when fixing #43243 .
When
BatchResolveLocks
meets a pessimistic lock, it callsresolvePessimisticLock
immediately, before callinggetTxnStatus
, considering that we will delete pessimistic locks no matter what state it's belonging transactions are:https://github.com/tikv/client-go/blob/fbec0230608310ecd18caaea76c0cdbb23cc933a/txnkv/txnlock/lock_resolver.go#L248-L266
However, it's not noticed that
resolvePessimisticLocks
ignores primary locks (to be more precise, locks whoseprimary
field points to itself), considering thatCheckTxnStatus
must has been called on it:https://github.com/tikv/client-go/blob/fbec0230608310ecd18caaea76c0cdbb23cc933a/txnkv/txnlock/lock_resolver.go#L1178-L1181
This may cause that in some rare cases, some pessimistic locks may be left after GCing.
The problem usually happen when node crashing, RPC failing, etc. so that transactions are leaving uncleared locks, which are not common cases. Once it happens, it will possibly affect the lagging of CDC and stale read.
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